1. Field of the Invention
The present invention relates to a disc unit and more particularly a disc unit in which a plurality of disc drive mechanism each driving a respective disc, are connected in the form of a daisy chain.
2. Description of the Prior Art
The magnetic disc units such as floppy disc units have been widely used as an external storage devices for computers, word processors and the like. For example, a disc unit including a plurality of magnetic heads is diclosed in U.S. Pat. No. 3,911,484, and a disc unit including a plurality of discs is disclosed in U.S. Pat. No. 4,563,715. FIG. 1 illustrates an arrangement in which a plurality of magnetic disc drive mechanism are connected to an data processing unit which is a host unit.
In FIG. 1, reference numeral 2 represents a control circuit of the data processing unit, which comprises special ICs. The information processing unit is connected through this control circuit 2 to a plurality of floppy disc drive mechanisms 1a and 1b in the case of FIG. 1 (but many floppy disc drive mechanisms may be included as indicated by 1c and 1d).
First, the arrangement of the magnetic disc drive mechanisms 1a will be described. A floppy disc 11 mounted in a predetermined position in the disc drive mechanisms 1a is spun by a spindle motor 10. A magnetic head 14 is moved linearly in the radial direction on the substantially flat surface of the floppy disc 11 so that the head 14 can write data on or read data from tracks on the surface of a floppy disc 11. The magnetic head 14 is driven by a head driving motor 9, such as a step motor, and the position of the head 14 is determined by a rotational amount of the head driving motor 9. The head driving motor 9 in turn is controlled through a driver 7 by a drive control circuit 6.
A plurality of sensors are disposed around the floppy disc 11. These sensors comprises photosensors or the like to be described below.
First, reference numeral 8 represents a track-0-sensor. The track-0 sensor 8 is incorporated into the magnetic head driving system including the head driving motor 9 to detect that the magnetic head 14 is positioned at the track-0 (in general, the outermost track) of the floppy disc 11. An index sensor 12 detects an index hole formed at a portion of the driving system of the spindle motor 10 or at the floppy disc 11, and thereby the sensor 12 generates a pulse per rotation of the disc which is utilized as a sync signal in the data writing or reading mode.
The jacket or cassette of a floppy disc is formed with a write-protect notch for inhibiting the writing of data on the disc. A write-protect sensor 13 detects the notch condition, thereby prohibiting data from being written on the floppy disc 11 if the notch indicates it is write-protected.
The reading or writing of data by the magnetic head 14 is directly controlled by a read/write circuit 5 comprising an amplifier for amplifying the readout data or the writing data, an erasing circuit and so on. The above described motors and sensors are controlled by the drive control circuit 6. In response to a control signal from the data processing unit and to the states of the output signals from the sensors, the drive control circuit 6 controls the rotation of the head driving motor 9 and the spindle motor 10, and the reading/writing of the magnetic head through the read/write circuit 5.
The read/write circuit 5 is connected through an interface 4 and a connector 3 to the control circuit 2 of the data processing unit.
The magnetic disc drive mechanism 1b is substantially similar in arrangement to the magnetic disc drive mechanism 1a just described above. The same reference numerals with a prime are used in the magnetic disc drive mechanism 1b to designate those parts similar to the parts of the magnetic disc drive mechanism 1a.
In the above-described conventional arrangement, plurality of magnetic disc drive mechanisms 1a-1d (up to four drives) are connected by the daisy chain system. Next, the interchange of the signals between the data processing unit and the disc drive mechanisms will be described.
The power is supplied to respective disc drive mechanisms 1a-1d through a power supply line 15. In response to a selection signal transmitted through one of four signal lines 16, one of the magnetic disc drive mechanisms 1a-1d is selected. That is, when the data processing unit selects one of the magnetic disc drive mechanisms 1a-1d, one of the signal lines 16 is made active.
In general, the magnetic disc drive mechanisms are respectively provided with dip switchs for determining the acceptable selection signal. The interface 4 provides one of the four selection signals determined by such a dip switch through a drive select signal line 19 to the drive control circuit 6.
When the signal line 19 becomes active, the drive control circuit 6 carries out a process relative to writing data on or reading data from the floppy disc 11, and carries out other processes. Reference numeral 17 denotes a control signal line for transmitting an input signal to the disc drive, while reference numeral 18 denotes an output signal line for outputting the output signal from the disc drive.
In the case of the daisy chain connection system described above, the control mode by the data processing unit is applicable to each disc drive mechanism in the same manner, regardless of how many disc drive mechanism are connected.
In FIG. 1, the signal lines between the data processing unit and the disc drive mechanisms are branched, but in general, another connector on the side of the disc drive mechanisms is connected in parallel with the connector 3 so that the adjacent disc drive mechanisms are connected in parallel through a cable, which includes the signal lines by utilizing the firstmentioned connector. In the case of the above-described arrangement, the number of the disc drive mechanisms can be increased in a simple manner up to the number of the selection signal lines. Furthermore, the data information unit can select a desired one of a plurality of disc drive mechanisms without the need of special control.
However, in the case of the arrangement described above with reference to FIG. 1, as is clear from the arrangement of the magnetic disc drive mechanism 1b, all of the connected disc drive mechanismsmust have circuits which can operate independently. Therefore each of the disc drive mechanisms which are mounted within the data processing unit or are disposed outside it must be provided with two connectors 3 and one or more cables. Furthermore, each disc drive mechanism must comprise an internal circuit operating independently. As a result, the arrangement of the conventional disc unit is complicated, so that the disc unit is expensive and the above-described arrangement does not utilize space efficiently.